In recent years, a laser beam processing unit, which carries out cutting or surface (heat) treating processes on several types of materials such as metal, by utilizing energy of high power laser beam produced from, e.g., a CO.sub.2 gas laser, has been put to practical use. Laser beams have high directivity and can concentrate energy onto a small area, therefore the laser beam processing unit can correctly and easily bore micro-diameter holes or cut a complex two-dimensional pattern, and also can process fragile or flexible materials. Moreover, a surface hardening process such as tempering for surfaces of metallic materials or a marking process can be carried out by properly controlling the heating energy and the heating time. A surface hardening process by a laser beam can include coating, alloying, pulse hardening, etc., in addition to heat treatment such as tempering, can be a precision process for a small area, and has the advantage of a very short processing time that can minimizing thermal stress and strain. Further, the cutting and surface treating processes can be successively carried out with a single laser beam processing unit, without using a heating furnace or cooling device, by controlling the heating energy and the heating time.
This kind of laser beam processing unit is generally expensive regarding power requirements, and a laser beam can act only at a point near to the focus point, thus the laser beam processing unit is unsuitable for cutting thick plate or complex three-dimensional workpieces. Therefore, when a three-dimensional metallic workpiece must be cut and subsequently surface hardened, it is difficult to subsequently carry out this work by single laser beam processing unit, so that it is preferable to use a machine tool for a machining process.
In the case where a machining process by machine tool and a laser beam process by laser beam processing unit must be successively carried out, several provisions have been made for facilitating automation and for improving working efficiency. For example, a compound machining shop has been suggested, in which a plurality of workpieces are successively transported on a conveyor path and a cutting work head and a laser beam work head are placed at each position along the conveyor path, and thus the compound machining shop can successively carry out a compound process consisting of a cutting process and a laser beam process on one workpiece.
The above-mentioned compound machining shop is one that automatically conveys workpieces to the cutting work head and the laser beam work head, and rapidly and successively carries out the cutting process and the laser beam process. However, because of the lack of consideration for carrying out rational and optimum process to the workpiece, there are some cases where the operation is not effective due to a shape of a workpiece to be processed or a processing type to be required. For example, in the case where the workpiece is most efficiently processed by procedure in which the rough profile thereof is formed by a laser beam cutting process, and then, a boring process or precise three-dimensional process is carried out thereon by a cutting tool, and, after cleaning cutting-oil or chips, surface treatment process is carried out on the predetermined points thereof by laser beam, the above-mentioned compound machining shop is required to reverse the direction of the conveyor path, and this reduces the efficiency of the operation. Further, the compound machining shop does not have a definite construction as a single controllable unit, but is only a technical concept of a processing workshop having a cutting machine and a laser beam machine, each being arranged separately in a specified working area, and thus it has no practicality.